For years scientists have urged national leaders to tackle climate change, based on the assumption that prevention efforts would require the coordinated actions of entire nations to be effective. But as anyone who has watched the past 15 years of international climate negotiations can attest, most countries are still reluctant to take meaningful steps to lower their production of greenhouse gases, much less address issues such as how to help developing countries protect themselves from the extreme effects of climate change. Frustrated by the ongoing diplomatic stalemate, a number of urban leaders have decided to take matters into their own hands, adopting solutions that already exist or inventing new ones for limiting greenhouse gas emissions and preparing for the effects of ongoing global warming.

Mayors and urban managers are taking over because they have a keener sense about how changing weather patterns will affect their cities’ political and economic future. As Bärbel Dieckmann put it in 2007, when she was mayor of Bonn, Germany, “cities are already experiencing flooding, water shortages, heat waves, coastal erosion and ozone-related deaths.” Since the mid-1990s, according to a 2009 report, the number of intense hurricanes has been increasing in the Atlantic Ocean, and the size of wildfires has been growing in the western U.S. As temperatures continue to rise, such extreme events may become even more frequent and severe. Most of the world’s major metropolises were originally built on rivers or coastlines and are therefore subject to flooding from rising seas and instances of heavier rainfall.